The output of an internal combustion engine may be increased by compressing the air required for the combustion of the fuel with the aid of an exhaust-gas turbocharger, which is made up of a turbine and a compressor operated in the air intake of the internal combustion engine. Exhaust-gas turbochargers may have the disadvantage of a delayed and insufficient response characteristic at lower speeds of the internal combustion engine, especially in automotive drives. To improve the response characteristic of the exhaust-gas turbocharger, the exhaust-gas turbocharger may be boosted via an electrical auxiliary drive. This may be done, for example, with an electromotor integrated in the exhaust-gas turbocharger, which at low rotational speeds of the internal combustion engine assists in driving the shaft of exhaust-gas turbocharger. However, this may require not only a high loading capacity with respect to the electromotor's speed, but may also entail a high electrical power requirement due to the high inertia moments of the turbine of the exhaust-gas turbocharger.
To avoid these disadvantages, U.S. Pat. No. 6,029,452 for example, refers to running an electrically operated charge-air compressor, also referred to as electrically operated auxiliary supercharger (ES), in the air intake of the internal combustion engine, in series with a conventional exhaust-gas turbocharger. This has the advantage that the electrically operated auxiliary charger (ES) inserted separately into the air intake can be optimized to the lowest speed range of the internal combustion engine, and its power requirement may be markedly reduced due to the substantially lower moment of inertia and better efficiency.
However, it has been shown that simply turning such an electrical turbocharger or electrical auxiliary supercharger (ES) on or off may lead to fluctuations in the boost-pressure supply, accompanied by a corresponding irregular torque of the internal combustion engine. Another negative consequence of an on and off operation of such an electrical supercharger (ES) is that a high load may be placed on the vehicle electrical system.
The German patent reference DE-A 197 40 968 refers to ascertaining a setpoint value for the air-mass flow in the intake manifold as a function of driver command. The European patent reference EP 885 353 B1 refers to determining a setpoint throttle valve angle and a setpoint boost pressure value on the basis of the setpoint charge derived from the driver command.